1. Field of the Invention
The present invention relates to a transflective type liquid crystal display device substrate, a color filter substrate, and a liquid crystal display device having any one of these. The invention relates particularly to a color filter substrate optimal for oblique electric field driving, and a liquid crystal display device having this.
2. Description of the Related Art
In recent years, it has been desired about a thin display device such as a liquid crystal display to make an image quality higher, decrease a price, and save an electric power. A color filter for the liquid crystal display device is requested to have a sufficient color purity, a high contrast, flatness, and other properties for attaining a higher image-quality display.
In order to gain a high image-quality liquid crystal display, liquid crystal alignment modes or liquid crystal driving modes such as VA (vertically alignment), HAN (hybrid-aligned nematic), TN (twisted nematic), OCB (optically compensated bend), CPA (continuous pinwheel alignment) or the like are suggested. As a result, wide-viewing-angle and high-speed-response liquid crystal display device has been put into practical use.
The liquid crystal display device in the VA mode, wherein liquid crystal molecules are aligned in parallel with a plane of a substrate such as a glass substrate, gives a wide viewing angle and cope easily with high-speed response. The liquid crystal display device in the HAN mode is effective for giving a wide viewing angle. For the liquid crystal display device in the VA mode, HAN mode, or the like, higher-level for color filter flatness (evenness of a film thickness, and a decrease in irregularities in a front surface of the color filter) and an electrical property such as dielectric constant or the like, is requested. Such high image-quality liquid crystal display device pursue, as a main theme, a technique of making the liquid crystal cell thickness (liquid crystal layer thickness) thinner to decrease coloration when the device is viewed from an oblique direction.
About the VA mode, developments of various improved modes have been advanced, examples of the modes including MVA (multi-domain vertically alignment), PVA (patterned vertically alignment), VAECB (vertically alignment electrically controlled birefringence), VAHAN (vertical alignment hybrid-aligned nematic), and VATN (vertically alignment twisted nematic) modes. A liquid crystal display device in a vertical electric field mode such as the VA mode, in which a drive-voltage is applied along the thickness direction of their liquid crystals, has, as main themes, a higher-speed liquid crystal response, a wide viewing angle technique, and a higher transmittance. The MVA technique is a technique of creating plural rib-form projection or slits for overcoming a problem that vertically aligned liquid crystals are instable at a time of a liquid-crystal-drive-voltage applying (a direction in which the liquid crystals initially having vertical alignment to a front surface of a substrate are inclined at the time of the voltage-applying, is not easily settled); and is a technique of forming liquid crystal domains between these ribs, and further forming domains aligned in plural directions, thereby ensuring a wide viewing angle.
Japanese Patent No. 3957430 discloses a technique of using first and second alignment-regulating structures to form liquid crystal domains. Jpn. Pat. Appln. KOKAI Publication No. 2008-181139 discloses a technique of using optical alignment to form four liquid crystal domains. This patent literature discloses that the following are necessary for ensuring a wide viewing angle: alignment treatment to be conducted plural times, which is related to a strict control of a tilt angle (into, for example, 89 degrees) in each domain; and alignment axes different in angle from each other by 90°, when viewed in plan, in order to form the domains.
Japanese Patent Nos. 2859093 and 4364332 each disclose a technique of using a transparent electroconductive film (a transparent electrode, a display electrode or a third electrode) of the color filter substrate side, and first and second electrodes of the array substrate side to control vertically aligned liquid crystals by use of an oblique electric field. According to Japanese Patent No. 2859093, liquid crystals having a negative dielectric constant anisotropy are used. Japanese Patent No. 4364332 discloses, in the claims and the text of the specification thereof, liquid crystals having a positive dielectric constant anisotropy. Japanese Patent No. 4364332 never describes any liquid crystal having the negative dielectric constant anisotropy.
Japanese Patent No. 4167963 relates to a transflective type liquid crystal display device using the negative dielectric constant anisotropy, and discloses a technique of forming electrode slits (electrode openings) to a common electrode above a color filter and further forming convex regions over pixels that are transmission regions of the color filter.
Usually, a liquid crystal display device in the VA mode, the TN mode, or some other mode has a basic structure wherein liquid crystals are sandwiched between a color filter substrate having a common electrode, and a pixel electrode (for example, a transparent electrode formed into a comb-teeth-form pattern and connected electrically to a TFT element) for driving the liquid crystals and an array substrate. In this structure, a drive-voltage is applied between the common electrode of the color filter and the pixel electrode formed to the array substrate side to drive the liquid crystals. A transparent electroconductive film as the pixel electrode, or the common electrode on a surface of the color filter is usually a thin film of an electroconductive metal oxide, such as ITO (indium tin oxide), IZO (indium zinc oxide), or IGZO (indium gallium zinc oxide).
As a technique disclosing a color filter, for example, a blue pixel, green pixel, red pixel and black matrix, Jpn. Pat. Appln. KOKAI Publication No. 10-39128 discloses, for example, a technique of forming a transparent electroconductive film over a black matrix and color pixel, and further laminating an overcoat.